In recent developments in motor vehicle design, there is a tendency for all driver commands to be forwarded electrically only, using drive-by-wire. Drive-by-wire (DbW) designates a driving or controlling of a motor vehicle without mechanical transmission of force by operating elements, such as gas pedal, brake pedal, or steering wheel, of the motor vehicle to the corresponding actuating elements of the motor vehicle, such as the throttle valve, brakes, and/or steering of the motor vehicle. An example of a conventional DbW system is the so-called e-gas system. The controlling of the named functions takes place instead via electrical lines and servomotors or electromechanical actuators. For safety reasons, the actuating elements of the motor vehicle have to be permanently monitored in order to prevent malfunctioning, such as an undesired acceleration of the motor vehicle.
The monitoring can be realized according to a three-level design (cf. “Standardisiertes E-Gas Überwachungskonzept für Benzin and Diesel Motorsteuerungen [“Standardized e-gas monitoring design for gasoline and diesel engine control systems”],” work group EGAS, 5 Jul. 2013, version 5.5). A first level, the functional level, contains engine controlling functions, inter alia for realizing the requested engine torques, component monitoring, the diagnosis of the input and output quantities, and the controlling of the system reactions in case of recognized error. A second level, the function monitoring level, recognizes errored sequences in monitoring-relevant areas of the function software in level 1, inter alia by monitoring the calculated torques or the vehicle acceleration. In case of error, system reactions are triggered. A third level, the computer monitoring level, monitors whether the second level is operating correctly through a question-response communication. In case of error, the triggering of system reactions takes place independent of the function computer.
The three-level design can have a structure based on torque or based on acceleration.
A torque-based structure of the monitoring however does not have an intuitively understandable character, because the driver of the motor vehicle does not consciously control the torque. In addition, a complex physical model having many variables is required. In addition, there is a coupling between the functional level and the monitoring level via characteristic maps, input signals, and further interfaces. As a result, there is a high adaptation outlay for the monitoring level, because the characteristic maps, input signals, and interfaces have to be adapted.
In contrast, in an acceleration-based structure of the monitoring, the functional level and the monitoring level are decoupled from each other. In addition, in contrast to a torque-based structure an acceleration-based structure of the monitoring level contains different variables than does the functional level, because for example an activation of auxiliary components of the motor vehicle is not relevant for this type of monitoring. However, the acceleration-based structure also does not always have an intuitively understandable character. In addition, the monitoring level requires a complex physical model that is permanently calculated and therefore consumes computing resources of a microcontroller.
There is therefore a need for a method for monitoring a drive-by-wire system of a motor vehicle that is intuitively easy to understand and that preferably uses a small amount of computing resources. Moreover, this method should be easy to adapt to different variants, compared to the torque-based monitoring structure.